Women’s Health with Minoos Hosseinzadeh, M.D. Identifying Inheritable Genetic Diseases through PGD
In the May 2008 issue of OCPC magazine, in vitro fertilization (IVF) as a form of treatment for infertility patients was explored in detail. One of the many advantages of this procedure is that it enables reproductive endocrinologists and other fertility specialists to look at the chromosomal make-up of an embryo or fertilized egg. The use of preimplantation genetic diagnosis (PGD) in these patients can also help identify specific inheritable genetic abnormalities. In this manner, the results are available prior to the embryos being transferred or implanted into the uterus, thereby allowing for the preferred transfer of normal or unaffected embryos. Prior to the advent of PGD, testing was only available after pregnancy had been achieved through chorionic villus sampling (removal, and testing of a small piece of tissue from the placenta) and amniocentesis.
An Introduction to Preimplantation Genetic Diagnosis
In this procedure, the female patient still undergoes ovarian stimulation followed by harvesting and fertilization of the eggs, as detailed in last month’s issue. The embryos are then grown in a laboratory environment immersed in a special culture solution. Three days after the harvesting, the embryo typically has six to eight cells. At this point, an opening is created in the shell of the embryo and one of the cells is removed. This procedure is performed on all of the good quality embryos, and it is this one cell that undergoes the genetic testing that is indicated. The biopsied embryos remain in the culture medium. Two days later, the results are available and a decision can be made regarding which embryos should be transferred into the uterus.
Inheritable Conditions Diagnosed Using PGD
Preimplantation genetic screening has been used in patients who have a higher risk of having embryos that are genetically abnormal, such as in women with advanced maternal age, those with repeated miscarriages and repeated IVF failure. PGD is also indicated for couples at risk of transmitting sex-linked disorders, single gene defects, or chromosomal disorders to their offspring, such as:
Rett syndrome
a - thalassemia
Incontinentia pigmenti
b - thalassemia
Pseudohyperparathyroidism
Fanconi anemia
Vitamin D-resistant rickets
Gaucher disease
Cystic fibrosis
Phenylketonuria
Tay-Sachs disease
Fragile X syndrome
Sickle cell anemia
Duchenne muscular dystrophy
Huntington disease
Von Hippel-Lindau disease
Hemophilia
Marfan syndrome
Down syndrome
Osteogenesis imperfecta
BRCA 1 and 2 mutations associated with cancer risk
Retinitis pigmentosa
Spinal muscular dystrophy
Lesch-Nyhan syndrome
Although PGD is not without certain pitfalls, it has completely revolutionized the field of reproductive medicine – especially in cases of genetic diseases. Since its inception in 1988, researchers have sought to improve and expand on the procedure. The future of PGD may include the identification of genetic links to more common diseases like diabetes, endometriosis, hypertension, cardiovascular disease and more – thus, exerting control over the transmission of these diseases to the offspring, and potentially eliminating their genetic transmission within an entire family.
The Future of Genetic Disease Diagnosis
Newer techniques, such as comparative genomic hybridization, are becoming available that may increase the accuracy of results. The introduction of DNA chip technology allows for even more genes to be screened. This technique is also in its very early stages, but suggests a way for fertility specialists to increase the number of diseases that can be diagnosed, and the number of would-be parents that can benefit from PGD.
OCPC Readers: Email questions to Women’s Health with Dr. Minoos at DrMinoos@OCPCmagazine.com. ____________________________________________________________________________
Dr. Minoos Hosseinzadeh is a nationally recognized specialist in reproductive endocrinology at the largest and most-established locally-based fertility center in Orange County, Calif., Coastal Fertility Medical Center (http://www.coastalfertility.com). Double-board certified in Obstetrics and Gynecology and Reproductive Endocrinology & Infertility, she is also a member of the American Society of Reproductive Medicine, Society for Reproductive Endocrinology and Infertility, American College of Obstetrics and Gynecology and the Royal College of Physicians and Surgeons. She has presented at several national and international fertility meetings and authored numerous papers on hormone replacement therapy and age-related female infertility.
